Golf ball material and method of preparing the same

ABSTRACT

The invention provides a golf ball material which is a resin mixture composed of (a) an olefin-unsaturated carboxylic acid copolymer and/or an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymer having a weight-average molecular weight (Mw) of from 40,000 to 80,000 and a weight-average molecular weight (Mw) to number-average molecular weight (Mn) ratio of from 5.0 to 8.0, or a metal neutralization product thereof, (b) an olefin-unsaturated carboxylic acid copolymer and/or an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymer having a weight-average molecular weight (Mw) of from 120,000 to 200,000 and a weight-average molecular weight (Mw) to number-average molecular weight (Mn) ratio of from 6.0 to 9.5, or a metal neutralization product thereof, (c) an organic acid or a metal salt thereof, and (d) a basic inorganic metal compound for neutralizing at least 70 mol % of acid groups in components (a) to (c), which resin mixture has a Shore D hardness of from 30 to 50. The golf ball material of the invention is a low-hardness material. Golf balls in which an injection molding of the golf ball material is used as a cover material have an excellent rebound and durability.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending application Ser.No. 12/575,256 filed on Oct. 7, 2009, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a golf ball material which is suitablefor use as a cover material in golf balls, has good flow properties andmoldability, and endows the golf ball with an excellent reboundresilience and durability even when the material hardness is low. Theinvention also relates to a method of preparing such a golf ballmaterial.

Ionomers are conventionally used in golf balls. Approaches being carriedout recently to achieve a higher ball rebound in particular includemethods that involve blending ionomers together, methods in which otherthermoplastic resins and additives are blended together with an ionomer,and methods that increase the degree of neutralization of an ionomeritself.

Among methods that involve blending ionomers together, a number oftechniques which use two types of ionomers having differentweight-average molecular weights have been proposed. For example, U.S.Pat. No. 7,462,113 discloses the use in a cover material of a ternaryionomer having a weight-average molecular weight of from 80,000 to500,000 in combination with a ternary ionomer having a weight-averagemolecular weight of from 2,000 to 30,000. Also, U.S. Pat. Nos. 7,273,903and 7,488,778 describe blending together, as a cover material: a ternaryionomer having a weight-average molecular weight of from 80,000 to500,000, a binary ionomer having a weight-average molecular weight offrom 2,000 to 30,000, and an optional thermoplastic elastomer.

However, the above proposed ionomer blending techniques all use resins(ionomers) that have been neutralized beforehand with metal ions,resulting in a lower degree of freedom in blend design—such as the typesof metal ions, the blending amounts, and the degrees ofneutralization—which has made it difficult to achieve the desiredproperties.

When use is made of a highly neutralized material in which the degree ofionomer neutralization has been increased, such a material tends to havea higher hardness, as a result of which the rebound resilience of thematerial has a tendency to increase. Conversely, efforts to lower thehardness of a highly neutralized ionomer lead to a diminution of thehigh rebound resilience characteristic of highly neutralized ionomericmaterials, which poses a challenge. Recently, various art has beendisclosed which, by softening the cover material used in a golf ball,improves the feel of the ball upon impact and also increases the spinrate on approach shots, thus enhancing the controllability. However,when the cover is soft, the ball has a poor rebound and a spinrate-lowering effect cannot be achieved, as a result of which the balltends to travel a shorter distance.

Accordingly, there exists a desire for, in cases where a highlyneutralized ionomeric material with the advantage of having a highdegree of freedom in blend design is used as the cover material, a golfball material which enables a high golf ball rebound and durability tobe retained even when the material hardness is low.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a golfball material which has a low material hardness and which, when shapedby injection molding and used as a golf ball cover, endows the golf ballwith excellent rebound and durability. Another object of the inventionis to provide a method for preparing such a golf ball material.

As a result of extensive investigations, the inventors, in preparingionomeric resin compositions having a low Shore D hardness of from 30 to50, focused on the weight-average molecular weight (Mw) andweight-average molecular weight (Mw)/number-average molecular weight(Mn) of the olefin-unsaturated carboxylic acid copolymer and/orolefin-unsaturated carboxylic acid-unsaturated carboxylic acid estercopolymer which serve as the base resin of an ionomer, blending twotypes of ionomers or the base resins thereof, then adding thereto anorganic acid or a metal salt thereof, adding also a metal ionic species,and carrying out an acid neutralization reaction. The inventorsdiscovered that golf balls in which the resulting resin compositions areinjection-molded and used as, for example, a cover material, exhibit anunexpectedly outstanding rebound and durability in spite of the lowhardness of the composition. This discovery ultimately led to thepresent invention.

Accordingly, the present invention provides the following golf ballmaterial and method of preparation.

[1] A golf ball material which is a resin mixture comprising:

(a) an olefin-unsaturated carboxylic acid copolymer and/or anolefin-unsaturated carboxylic acid-unsaturated carboxylic acid estercopolymer having a weight-average molecular weight (Mw) of from 40,000to 80,000 and a weight-average molecular weight (Mw) to number-averagemolecular weight (Mn) ratio of from 5.0 to 8.0, or a metalneutralization product thereof,

(b) an olefin-unsaturated carboxylic acid copolymer and/or anolefin-unsaturated carboxylic acid-unsaturated carboxylic acid estercopolymer having a weight-average molecular weight (Mw) of from 120,000to 200,000 and a weight-average molecular weight (Mw) to number-averagemolecular weight (Mn) ratio of from 6.0 to 9.5, or a metalneutralization product thereof,

(c) an organic acid or a metal salt thereof, and

(d) a basic inorganic metal compound for neutralizing at least 70 mol %of acid groups in components (a) to (c); wherein the resin mixture has aShore D hardness of from 30 to 50.

[2] The golf ball material of [1] which has a mixing ratio by weight(a):(b) between component (a) and component (b) of from 10:90 to 70:30,and wherein component (c) is included in an amount of from 5 to 35 partsby weight per 100 parts by weight of components (a) and (b) combined.[3] The golf ball material of [1], wherein the organic acid of component(c) is selected from the group consisting of stearic acid, oleic acid,and mixtures thereof.[4] The golf ball material of [1], wherein the unsaturated carboxylicacid of components (a) and (b) is acrylic acid or methacrylic acid.[5] A method of preparing a gold ball material, the method comprisingthe step of preparing the golf ball material of [1] using a single-screwextruder, a twin-screw extruder, or a tandem extruder thereof.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described more fully below.

The golf ball material of the invention contains as the base resins: (a)an olefin-unsaturated carboxylic acid copolymer and/or anolefin-unsaturated carboxylic acid-unsaturated carboxylic acid estercopolymer having a weight-average molecular weight (Mw) of from 40,000to 80,000 and a weight-average molecular weight (Mw) to number-averagemolecular weight (Mn) ratio of from 5.0 to 8.0, or a metalneutralization product thereof, and (b) an olefin-unsaturated carboxylicacid copolymer and/or an olefin-unsaturated carboxylic acid-unsaturatedcarboxylic acid ester copolymer having a weight-average molecular weight(Mw) of from 120,000 to 200,000 and a weight-average molecular weight(Mw) to number-average molecular weight (Mn) ratio of from 6.0 to 9.5,or a metal neutralization product thereof.

The weight-average molecular weight (Mw) of above component (a) is from40,000 to 80,000, and preferably from 45,000 to 70,000. Theweight-average molecular weight (Mw) to number-average molecular weight(Mn) ratio is from 5.0 to 8.0, and preferably from 5.5 to 7.0.

The weight-average molecular weight (Mw) of component (b) is from120,000 to 200,000, and preferably from 120,000 to 180,000. Theweight-average molecular weight (Mw) to number-average molecular weight(Mn) ratio is from 6.0 to 9.5, preferably from 6.1 to 9.0, and morepreferably from 6.1 to 8.5.

When the above two types of resin components (a) and (b) of differingaverage molecular weights and differing molecular weight distributions(Mw/Mn) are blended in this way, the low-molecular-weight andhigh-molecular-weight polymers complexly intertwine, giving rise tomolecular synergistic effects. By additionally increasing the degree ofneutralization thereof, even when the resin mixture has a low hardness,it is possible to achieve a high ball rebound and durability.

The weight-average molecular weight (Mw) and the number-averagemolecular weight (Mn) are values calculated relative to polystyrene ingel permeation chromatography (GPC). A word of explanation is neededhere concerning GPC molecular weight measurement. It is not possible todirectly take GPC measurements for binary copolymers and ternarycopolymers because these molecules are absorbed to the GPC column owingto the unsaturated carboxylic acid groups within the molecule. Instead,the unsaturated carboxylic acid groups are generally converted toesters, following which GPC measurement is carried out and thepolystyrene-equivalent average molecular weights Mw and Mn arecalculated.

The olefin used in above component (a) or (b) preferably has from 2 to 6carbons, and is most preferably ethylene. The unsaturated carboxylicacid used in component (a) or (b) is exemplified by acrylic acid (AA)and methacrylic acid (MAA), although the use of methacrylic acid (MAA)is especially preferred. The unsaturated carboxylic acid ester used incomponent (a) or (b) is preferably a lower alkyl ester, and mostpreferably butyl acrylate (n-butyl acrylate, i-butyl acrylate).

The unsaturated carboxylic acid content (acid content) in component (a)or (b), while not subject to any particular limitation, is in a range ofpreferably at least about 2 wt but not more than about 15 wt %, and morepreferably at least about 2 wt % but not more than about 12 wt %. If theacid content is lower than this range, moldings of the golf ballmaterial may not be able to achieve a good rebound. On the other hand,if the acid content is too high, such moldings may become excessivelyhard, adversely affecting the durability.

In this invention, it is essential to use component (a) and component(b) together. The mixing ratio by weight (a):(b) between component (a)and component (b) is preferably from 10:90 to 70:30, and more preferablyfrom 10:90 to 60:40. If the proportion of component (b) is higher thanthe above range, the hardness may increase and the material may becomedifficult to mold.

In cases where the metal neutralization products of resins (i.e.,ionomers) are used as component (a) and component (b), the type of metalneutralization product and the degree of neutralization are not subjectto any particular limitation. Illustrative examples include 60 mol %zinc (degree of neutralization with zinc) ethylene-methacrylic acidcopolymers, 40 mol % magnesium (degree of neutralization with magnesium)ethylene-methacrylic acid copolymers, and 40 mol % magnesium (degree ofneutralization with magnesium) ethylene-methacrylic acid-isobutyleneacrylate terpolymers.

In the present invention, it is especially preferable to use ascomponent (a) and component (b) an un-neutralized olefin-unsaturatedcarboxylic acid copolymer and/or an un-neutralized olefin-unsaturatedcarboxylic acid-unsaturated carboxylic acid ester copolymer.

As mentioned above, copolymers or ionomers having a weight-averagemolecular weight (Mw) and a molecular weight distribution breadth(U=Mw/Mn) set within specific ranges are used as components (a) and (b).For example, use may be made of commercial products from the Nucrelseries (produced by DuPont-Mitsui Polychemicals Co., Ltd.) or the Escorseries (produced by ExxonMobil Chemical).

The organic acid or metal salt thereof serving as component (c), whilenot subject to any particular limitation, is preferably one or moreselected from the group consisting of stearic acid, behenic acid, oleicacid, maleic acid and metal salts thereof. One selected from the groupconsisting of stearic acid, oleic acid and mixtures thereof isespecially preferred. The organic acid metal salt of component (c) ispreferably a metallic soap. The metal salt makes use of metal ionshaving a valence of from 1 to 3 which are preferably selected from thegroup consisting of lithium, sodium, magnesium, aluminum, potassium,calcium and zinc. A metal salt of stearic acid is especially preferred.Specifically, the use of magnesium stearate, calcium stearate, zincstearate or sodium stearate is preferred. Of these, the use of magnesiumstearate is especially preferred.

Component (c) is included in an amount, per 100 parts by weight ofcomponents (a) and (b) as the base resins, of preferably from 5 to 35parts by weight, and more preferably from 10 to 28 parts by weight. Ifcomponent (c) is included in too small an amount, lowering the hardnessof the resin material will be difficult. Conversely, too much component(c) will make the resin material difficult to mold and will increasebleeding at the material surface, affecting the molded article.

Illustrative examples of the metal ions in the basic inorganic metalcompound of above component (d) include Na⁺, K⁺, Li⁺, Zn²⁺, Ca²⁺, Mg²⁺,Cu²⁺ and Co²⁺. Of these, Na⁺, Ca²⁺ and Mg²⁺ are preferred, and Mg²′ isespecially preferred. These metal salts may be introduced into the resinusing, for example, formates, acetates, nitrates, carbonates,bicarbonates, oxides or hydroxides.

The basic inorganic metal compound of (d) above is a component forneutralizing acid groups in above components (a) to (c). The amount ofcomponent (d) included is set to at least 70 mol %, based on the acidgroups in above components (a) to (c). Here, the amount in which thebasic inorganic metal compound of component (d) is included may beselected as appropriate for obtaining the desired degree ofneutralization. Although this amount depends also on the degree ofneutralization of components (a) and (b) that are used, in general it ispreferably from 0.5 to 10 parts by weight, and more preferably from 1 to5 parts by weight, per 100 parts by weight of components (a) and (b)combined. The degree of neutralization of acid groups in abovecomponents (a) to (c) must be at least 70 mol %, and is preferably atleast 90 mol %, and more preferably at least 100 mol %.

The resin composition made up of above components (a) to (d) accountsfor at least about 50 wt %, preferably at least about 60 wt %, morepreferably at least about 70 wt %, and most preferably at least about 90wt %, of the overall golf ball material.

The following thermoplastic resins may be included in the golf ballmaterial of the invention, insofar as the objects of the invention areattainable. Illustrative, non-limiting, examples of thermoplastic resinsthat may be used include polyolefin elastomers (including polyolefinsand metallocene polyolefins), polystyrene elastomers, diene polymers,polyacrylate polymers, polyamide elastomers, polyurethane elastomers,polyester elastomers and polyacetals.

In addition, the golf ball material of the invention may also includeoptional additives as appropriate for the intended use. For example,when the inventive golf ball material is to be used as a cover material,various additives such as pigments, dispersants, antioxidants,ultraviolet absorbers and light stabilizers may be added to abovecomponents (a) to (d). When such additives are included, they may beadded in an amount of generally at least about 0.1 part by weight, andpreferably at least about 0.5 part by weight, but generally not morethan about 10 parts by weight, and preferably not more than about 4parts by weight, per 100 parts by weight of above components (a) to (d)combined.

The melt flow rate (MFR) of the inventive golf ball material, asmeasured in accordance with JIS-K7210 at a test temperature of 190° C.and a test load of 21.18 N (2.16 kgf), is not subject to any particularlimitation. However, to provide good flow properties and moldability atthe time of injection molding, it is recommended that the melt flow ratebe preferably at least about 3.0 g/10 min, more preferably at leastabout 3.5 g/10 min, and even more preferably at least about 4.0 g/10min, but preferably not more than about 10.0 g/10 min, and morepreferably not more than about 8.0 g/10 min.

Moldings obtained using the golf ball material of the invention have aShore D hardness of at least 30, preferably at least 33, and morepreferably at least 35, but not more than 50, and preferably not morethan 48.

The method of preparing the golf ball material of the present inventionis not subject to any particular limitation, although use may be made ofa method which involves charging the ionomers or un-neutralized polymersof components (a) and (b), together with component (c) and component(d), into a hopper and extruding under the desired conditions.Alternatively, component (c) may be charged from a separate feeder. Inthis case, the neutralization reaction by above component (d) as themetal cation source with the carboxylic acids in components (a), (b) and(c) may be carried out by various types of extruders. The extruder maybe either a single-screw extruder or a twin-screw extruder, although atwin-screw extruder is preferable. Alternatively, these extruders may beused in a tandem arrangement, such as single-screw extruder/twin-screwextruder or twin-screw extruder/twin-screw extruder. These extrudersneed not be of a special design; the use of existing extruders willsuffice.

The golf ball material of the invention may be used as the material fora one-piece golf ball, or may be used as a cover material or anintermediate layer material in a two-piece solid golf ball composed of acore and a cover encasing the core or in a multi-piece solid golf ballcomposed of a core of at least one layer, one or more intermediate layerencasing the core, and a cover of at least one layer encasing theintermediate layer. In the case of multilayer golf balls composed of acore of at least one layer and a cover of at least two layers inparticular, a golf ball of outstanding rebound and durability can beobtained when the core is formed of a rubber composition which includescis-1,4-polybutadiene, an unsaturated carboxylic acid metal salt, aninorganic filler and an organic peroxide; the material of the presentinvention is used in an inner cover which is not the outermost coverlayer; and a conventional ionomeric resin or a conventional polyurethaneelastomer is used as the cover.

As described above, the golf ball material of the present invention is ahighly neutralized ionomeric resin mixture in which two types ofcopolymers having weight-average molecular weights and molecular weightdistribution breadths (weight-average molecular weight/number-averagemolecular weight) set within different specific ranges serve as the baseresins to which is added an organic acid or a metal salt thereof, and aneutralizing basic inorganic metal compound. Golf balls in which aninjection molding made from the inventive golf ball material is used as,for example, a cover material have an excellent rebound and durabilityin spite of the low hardness.

EXAMPLES

The following Examples and Comparative Examples are provided by way ofillustration and not by way of limitation.

Examples 1 to 3 and Comparative Examples 1 to 3

Solid cores having a diameter of 37.50 mm and a weight of 32.80 g wereobtained using a core material of the following formulation and composedprimarily of cis-1,4-polybutadiene.

Core Formulation cis-1,4-Polybutadiene 100 parts by weight Zinc oxide 5parts by weight Barium sulfate 15 parts by weight Antioxidant 0.2 partby weight Zinc acrylate 25 parts by weight Dicumyl peroxide 1.0 parts byweight

Next, in each example, an intermediate layer material having thecomposition shown in Table 1 was mixed in a kneading-type twin-screwextruder at 200° C. to give a cover material in the form of pellets. Thepelletized material was then extruded within a mold in which the abovesolid core had been placed, thereby producing a sphere having anintermediate layer of 1.5 mm thickness.

A cover composition of Himilan 1605 and Himilan 1706 (both trade names)blended in a 50:50 weight ratio was then injection-molded as theoutermost layer (cover) material over the sphere, thereby producing athree-piece solid golf ball of the diameter and weight shown in Table 1.

The properties of the resulting golf balls in the respective examplesand comparative examples were evaluated as described below. The resultsare presented in Table 1.

TABLE 1 Comparative Example Example 1 2 3 1 2 3 (a) Polymer A 50 10 20 —50 100 (b) Polymer B 50 90 — 100 — — (b) Polymer D — — 80 100 — — —Polymer C — — — — 50 — (c) Magnesium 25 12 15 25 30 25 stearate (d)Magnesium oxide 3 3 3 3 3 3 Material moldability good good good goodgood NG Shore D hardness of material 47 41 42 52 53 40 Ball Diameter(mm) 42.72 42.73 42.71 42.73 42.76 42.73 properties Weight (g) 45.3545.23 45.28 45.27 45.26 45.26 10-130 kgf 2.77 2.97 2.94 2.65 2.63 3.08deflection (mm) Initial velocity 76.30 75.80 76.15 75.90 76.30 75.24(m/s) Durability good good good NG NG good Ingredient amounts shownabove are in parts by weight.

The materials in the above table are explained below.

Polymer A

Trade name: Nucrel N1050H

An un-neutralized ethylene-methacrylic acid binary copolymer (availablefrom DuPont-Mitsui Polychemicals Co., Ltd.). Weight-average molecularweight (Mw), 61,000; molecular weight distribution (Mw/Mn), 6.13.

Polymer B

Trade name: Nucrel N0200H

An un-neutralized ethylene-methacrylic acid binary copolymer (availablefrom DuPont-Mitsui Polychemicals Co., Ltd.). Weight-average molecularweight (Mw), 132,000; molecular weight distribution (Mw/Mn), 8.43.

Polymer D

Trade name: Nucrel AN4318

An un-neutralized ethylene-methacrylic acid-unsaturated carboxylic acidester ternary copolymer (available from DuPont-Mitsui Polychemicals Co.,Ltd.). Weight-average molecular weight (Mw), 183,000; molecular weightdistribution (Mw/Mn), 6.14.

Polymer C

Trade name: Nucrel

An un-neutralized ethylene-methacrylic acid-unsaturated carboxylic acidester ternary copolymer (available from DuPont-Mitsui Polychemicals Co.,Ltd.). Weight-average molecular weight (Mw), 127,000; molecular weightdistribution (Mw/Mn), 4.37.

The molecular weights and molecular weight distributions of each of theabove polymers were determined by measurement using gel permeationchromatography (GPC), followed by calculation of thepolystyrene-equivalent values.

Magnesium Stearate

Available under the trade name Magnesium Stearate G from NOFCorporation.

The physical properties of the golf ball materials and the golf ballswere measured as follows.

Material Moldability

Golf ball materials which had a melt flow rate, as measured inaccordance with JIS-K 7210 at a temperature of 190° C. and a load of21.18 N (2.16 kgf), within a range of from 3 to 10 g/10 min were ratedas “good,” and materials which had a melt flow rate outside of thisrange were rated as “NG.”

Shore D Hardness of Material

The composition was molded into sheets having a thickness of 2 mm, threesuch sheets were stacked together, and the hardness was measured with aShore D durometer.

Deflection (mm)

The golf ball was placed on a steel plate and the deflection (mm) by theball when compressed under a final load of 1,275 N (130 kgf) from aninitial load of 98 N (10 kgf) was measured. This test was carried out at23±1° C.

Initial Velocity (m/s)

The initial velocity of the ball was measured using an initial velocitymeasuring apparatus of the same type as the USGA drum rotation-typeinitial velocity instrument approved by the R&A. The ball was heldisothermally at a temperature of 23±1° C. for at least 3 hours, thentested at the same temperature. The ball was hit using a 250-pound(113.4 kg) head (striking mass) at an impact velocity of 143.8 ft/s(43.83 m/s). Ten balls were each hit twice. The time taken by the ballto traverse a distance of 6.28 ft (1.91 m) was measured and used tocompute the initial velocity of the ball. This cycle was carried outover a period of about 15 minutes.

Durability on Repeated Impact

The durability of the golf ball was evaluated using an ADC Ball CORDurability Tester produced by Automated Design Corporation (U.S.). Theball was fired using air pressure and made to consecutively strike twometal plates arranged in parallel. Using the average number of shotsrequired for the ball to crack, the durability was rated according tothe criteria indicated below. (Average values were obtained byfurnishing four balls of the same type for testing, repeatedly firingeach of the four balls until it cracked, and averaging the number ofshots required for the respective balls to crack. The type of testerused was a vertical COR durability tester, and the incident velocity ofthe balls on the metal plates was 43 m/s.)

Good: More than 150 shots

Fair: 100 to 150 shots

NG: Less than 100 shots

As is apparent from the results in Table 1 above, the golf ballsobtained in Comparative Examples 1 to 3 had the following drawbacks.

In Comparative Example 1, component (b) was used alone as the baseresin, and the material hardness was high. Compared with Examples 1 and2 according to the invention, the ball had a lower rebound and a poordurability.

In Comparative Example 2, two different types of copolymers were used,but a polymer which did not satisfy the component (a) and component (b)conditions was used as Polymer C. The material hardness was high and,compared with Examples 1 and 2 of the invention, the ball had a lowerinitial velocity and a lower durability.

In Comparative Example 3, component (a) was used alone as the baseresin. The flowability was too high, resulting in a poor moldability. Inaddition, the golf ball material did have a lower hardness, but theinitial velocity of the ball was much lower than in the examplesaccording to the invention.

1. A golf ball material which is a resin mixture comprising: (a) anolefin-unsaturated carboxylic acid copolymer and/or anolefin-unsaturated carboxylic acid-unsaturated carboxylic acid estercopolymer having a weight-average molecular weight (Mw) of from 40,000to 80,000 and a weight-average molecular weight (Mw) to number-averagemolecular weight (Mn) ratio of from 5.0 to 8.0, or a metalneutralization product thereof, (b) an olefin-unsaturated carboxylicacid copolymer and/or an olefin-unsaturated carboxylic acid-unsaturatedcarboxylic acid ester copolymer having a weight-average molecular weight(Mw) of from 120,000 to 200,000 and a weight-average molecular weight(Mw) to number-average molecular weight (Mn) ratio of from 6.0 to 9.5,or a metal neutralization product thereof, (c) an organic acid or ametal salt thereof, and (d) a basic inorganic metal compound forneutralizing at least 70 mol % of acid groups in components (a) to (c);wherein the resin mixture has a Shore D hardness of from 30 to
 50. 2.The golf ball material of claim 1 which has a mixing ratio by weight(a):(b) between component (a) and component (b) of from 10:90 to 70:30,and wherein component (c) is included in an amount of from 5 to 35 partsby weight per 100 parts by weight of components (a) and (b) combined. 3.The golf ball material of claim 1, wherein the organic acid of component(c) is selected from the group consisting of stearic acid, oleic acid,and mixtures thereof.
 4. The golf ball material of claim 1, wherein theunsaturated carboxylic acid of components (a) and (b) is acrylic acid ormethacrylic acid.
 5. A method of preparing a gold ball material, themethod comprising the step of preparing the golf ball material of claim1 using a single-screw extruder, a twin-screw extruder, or a tandemextruder thereof.